JP4765347B2 - Electrical steel sheet - Google Patents

Description

  The present invention relates to an electromagnetic steel sheet used for an iron core of an electric motor or a generator or an iron core of a stationary machine such as a transformer or a reactor, and more particularly to an electromagnetic steel sheet having a low iron loss in a high frequency range of about 400 Hz to 2 kHz and a manufacturing method thereof. It is.

  Motors used in electric devices, electric vehicles, and the like are being adopted at higher rotational speeds than before in order to cope with the reduction in size and weight. Also, multi-pole rotors are being adopted for magnet motors in order to improve torque and reduce torque ripple. In such a high-speed rotation or multi-pole rotor motor, the drive frequency tends to increase as the number of rotations and the number of poles increase. Therefore, it has been emphasized that the magnetic steel sheet used for the iron core of such a motor is excellent in magnetic properties in a high frequency range, particularly in a high frequency range of about 400 Hz to 2 kHz. That is, this frequency range corresponds to the drive frequency of the motor, and a high frequency component (same frequency range) of several times the drive frequency is superimposed on the drive frequency during driving.

  By the way, when the iron core is magnetized at a high frequency, it is known that energy loss increases due to an increase in eddy current loss. In order to prevent this, it is effective to increase the specific resistance of the electromagnetic steel sheet that is the material of the iron core or to reduce the plate thickness. However, in order to increase the specific resistance of electrical steel sheets, it is necessary to add a large amount of specific resistance increasing elements such as Si, Al, Cr, Mn, etc., which increases production costs due to increased raw material costs and increased rolling load. Invite the rise. Furthermore, there is a problem that the punching cost for the user is increased due to the increase in hardness of the steel plate. On the other hand, reducing the plate thickness causes an increase in manufacturing costs in the rolling process and the annealing process, and causes problems such as difficulty in handling by the user due to a decrease in rigidity of the steel sheet.

  Therefore, a technique for reducing eddy current loss that is different from the increase in the specific resistance and the reduction in the plate thickness has been proposed. For example, Patent Document 1 proposes a technique for controlling the average crystal grain size to 5 to 60 μm, which is smaller than a conventional appropriate value, while setting the plate thickness to 0.10 to 0.25 mm. However, this technology only specifies the optimum crystal grain size for iron loss in the high frequency range, and since it is inevitable that the magnetic permeability decreases and the hysteresis loss increases as the crystal grain size becomes finer. On the other hand, there is a problem that iron loss increases remarkably. Patent Document 2 discloses a technique for controlling the crystal grain size of the outermost layer thickness within a proper range, paying attention to the role of hysteresis loss. However, this technique pays attention to the hysteresis loss of the crystal grains in contact with the surface of the steel sheet, and only seeks an appropriate range for the relationship between the crystal grain size and the crystal grain size inside the plate thickness. It is difficult to effectively reduce eddy currents that are problematic in the high frequency range.

As another technique for reducing iron loss in a high-frequency region, for example, in Patent Documents 3 and 4, a sheet thickness surface layer portion is obtained by performing a siliconizing treatment from the surface of the steel sheet and imparting a Si concentration gradient in the sheet thickness direction. Has been disclosed to reduce the iron loss as a whole of the plate thickness in the high frequency region by increasing the magnetic permeability of the plate and concentrating the magnetic flux on the surface layer portion of the plate thickness. However, this technique has a problem of an increase in manufacturing cost and a decrease in productivity due to the siliconization treatment. Moreover, since the increase in the Si content in the steel sheet surface layer increases the hardness of the steel sheet, there is also a problem of promoting the wear of the iron core punching die for the user.
Japanese Patent Laid-Open No. 03-223445 Japanese Patent Laid-Open No. 06-073511 JP 11-256289 A JP 11-293423 A

  As described above, in the conventional technique in which the specific resistance is increased, the thickness is reduced, or the Si concentration gradient is applied in the thickness direction of the steel plate, iron loss is stably generated in a high frequency range, particularly in a high frequency range of about 400 Hz to 2 kHz. Actually, it is difficult to obtain a low electrical steel sheet at low cost.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to propose an electrical steel sheet that stably exhibits low iron loss characteristics in a high frequency range of about 400 Hz to 2 kHz and an inexpensive manufacturing method thereof. is there.

  In order to develop an electromagnetic steel sheet that stably exhibits a low iron loss in a high frequency range of about 400 Hz to 2 kHz, the inventors have used a method different from the conventional technique in which a Si concentration gradient is imparted in the thickness direction of the electromagnetic steel sheet. A method for providing a distribution of magnetic permeability in the thickness direction was studied. And in the non-oriented electrical steel sheet, the magnetic permeability depends on the crystal grain size, and paying attention to the fact that the larger the crystal grain size, the higher the magnetic permeability. In addition, a high-permeability region consisting of a coarse crystal grain structure and a low-permeability region consisting of a fine crystal grain structure are arranged at the center of the plate thickness, and the thickness and average crystal grain size are controlled within an appropriate range. As a result, it was found that the magnetic flux can be concentrated on both surface layers of the steel sheet, and consequently, iron loss in a high frequency range of about 400 Hz to 2 kHz can be reduced, and the present invention has been completed.

That is, the present invention is an electrical steel sheet containing 0.010 mass% or less of C and 4 mass% or less of Si, and both surface layer portions of the steel sheet have coarse crystal grain portions defined as follows: The center part in the plate thickness direction has a fine crystal grain part defined as follows, and the ratio of the average crystal grain size between the coarse crystal grain part and the fine crystal grain part is 2.0 or more. The total thickness of both surface layer portions of the coarse crystal grain portion is 10% or more of the total plate thickness, and the thickness of the fine crystal grain portion is 10% or more of the total plate thickness (however, the plate thickness is 0.00 . Except for those having a thickness of 08 to 0.22 mm .)
When the distribution in the thickness direction of the average grain size D in a plane parallel to the surface of the steel sheet is measured, the maximum value is D _max and the minimum value is D _min .
Coarse crystal grain part: part satisfying D ≧ 0.5D _max Fine crystal grain part: part satisfying D ≦ 2.0 D _min

  The coarse crystal grain portion in the electrical steel sheet of the present invention has a difference in thickness between both surface layer portions of 30% or less of the average thickness of both surface layer portions, and a difference in average crystal grain size between both surface layer portions. The average crystal grain size is 30% or less.

According to the present invention, it is possible to provide an electromagnetic steel sheet having a low iron loss in a high frequency range of about 400 Hz to 2 kHz at a low cost.

  The inventors have established a stable distribution in the high-frequency region by providing a distribution in the magnetic permeability in the thickness direction, which is different from the prior art in which the Si concentration gradient is imparted in the thickness direction of the steel plate and by a cheap method. In order to develop an electrical steel sheet with low loss, the difference in permeability depending on the crystal grain size, i.e., in the non-oriented electrical steel sheet having a smaller crystal grain size compared to the grain oriented electrical steel sheet, the permeability increases as the crystal grain size increases. We focused on the improvement of magnetic susceptibility and studied repeatedly. As a result, it is possible to concentrate the magnetic flux on both surface layers of the steel sheet and to effectively reduce the iron loss in the high frequency region by arranging coarse crystal grain structures with high magnetic permeability on both surface layers on the front and back sides of the electromagnetic steel sheet. I came up with it. In addition, since the coarse crystal grain structure has a small hysteresis loss, it is possible to effectively reduce the hysteresis loss even when the magnetic flux is concentrated on the plate thickness surface layer by being excited at a high frequency by arranging this structure in the plate thickness surface layer portion. can do. That is, according to the present invention, the eddy current loss and the hysteresis loss in the high frequency region can be reduced at the same time, so that the iron loss can be effectively reduced. In addition, since the techniques of Patent Documents 3 and 4 described above are intended to reduce iron loss in a very high frequency range of 10 kHz, a magnetic permeability difference of twice or more is provided between the surface layer and the inside of the steel sheet. However, since the present invention is intended for electromagnetic steel sheets used for motor cores, reactors, etc. used in a frequency range of about 400 Hz to 2 kHz, the surface layer / center layer permeability ratio is not less than twice. There is no need.

Hereinafter, the electrical steel sheet according to the present invention will be described.
Si: 4 mass% or less
Si is an element that reduces the eddy current loss by increasing the specific resistance of the steel sheet. When reducing iron loss in a high frequency range, it is necessary to add Si according to the assumed frequency range. However, if the Si addition amount exceeds 4 mass%, rolling becomes difficult and manufacturing becomes difficult, so the amount is limited to 4 mass% or less. A preferable Si range is 0.5 to 3.5 mass%. When reducing the eddy current loss by reducing the plate thickness, it is not necessary to add Si. Further, the present invention is not a technique for reducing iron loss by utilizing the difference in magnetic permeability in the plate thickness direction due to the Si concentration gradient, but the present invention can also be used in combination with the technology for providing the Si concentration gradient in the plate thickness direction. It does not interfere with the effect.

  In the electrical steel sheet of the present invention, the composition of components other than Si is not particularly limited, and may be in a range included in a normal electrical steel sheet. Specifically, as component composition other than Si, C: 0.010 mass% or less, Mn: 0.1 to 1.5 mass%, P: 0.5 mass% or less, S: 0.01 mass% or less, Al: 2.0 mass% or less, Ti: 0.010 mass% or less, Nb: 0.010 mass% or less, Sb: 0.020 mass% or less, Se: 0.020 mass% or less may be included.

Next, the steel sheet structure characterized by the magnetic steel sheet of the present invention will be described.
The present invention utilizes the fact that the coarse crystal grain structure has higher magnetic permeability and lower hysteresis loss than the fine grain structure, and reduces eddy current loss and hysteresis loss in a high frequency range of about 400 Hz to 2 kHz. This is a technique for reducing iron loss in the high frequency range. Therefore, in order to obtain the above effect, the electrical steel sheet of the present invention is a part made of a coarse crystal grain structure having a high magnetic permeability in the steel sheet surface layer part (hereinafter referred to as “coarse crystal grain part”), and the magnetic permeability in the steel sheet center part. It is essential to provide a portion (hereinafter referred to as “fine crystal grain portion”) having a low crystal grain structure having a low particle size.

Here, the coarse crystal grain part and the fine crystal grain part in the present invention determine the distribution in the thickness direction of the average grain diameter D in a plane parallel to the steel sheet surface of the electrical steel sheet, and the maximum of the average grain diameter D is obtained. When the value is D _max and the minimum value is D _min , the thickness direction region satisfying D ≧ 0.5D _max is defined as a coarse crystal grain portion, and the thickness direction region satisfying D ≦ 2.0 D _min is defined as a fine crystal grain portion. It is a thing.

The distribution in the plate thickness direction of the average particle diameter D in a plane parallel to the steel plate surface is measured as follows. FIG. 1 is a schematic diagram showing a cross-sectional view in the plate thickness direction (perpendicular to the rolling surface) of a steel plate having a coarser grain structure than that of the center portion of the steel plate, in which the grain size of both surface layers on the front and back sides of the steel plate is large. Is. First, after revealing the crystal grain boundary of the cross section of the steel plate by a method such as etching, a line segment L parallel to the rolling surface is drawn at an arbitrary position z in the plate thickness direction of the cross section. A value obtained by dividing the number N of intersecting crystal grain boundaries by the length of the line segment L is defined as an average crystal grain size D (z) at a position z in the plate thickness direction. That is, the average crystal grain size D (z) at the position in the plate thickness direction z is expressed by L / N. In addition,
If there is a difference in the average grain size D (z) between the rolling direction and the direction perpendicular to the rolling direction, the average of the two is taken.

Further, the average crystal grain size of the coarse crystal grain portion and the fine crystal grain portion in the electrical steel sheet of the present invention is obtained by further averaging the average crystal grain size D (z) of each region. That is, the coarse crystal grain portions existing in both surface layers on the front and back sides of the steel sheet are 1, 2, respectively, their thicknesses and their total thicknesses are t ₁ , t ₂ , (t ₁ + t ₂ ), plate thickness, respectively. When the fine crystal grain portion in the center is 3 and the thickness is t ₃ , the definition is as follows.
<D ₁ >: Average crystal grain size of coarse crystal grain part 1 = (1 / t ₁ ) ∫Coarse _{crystal grain part 1} D (z) dz
<D ₂ >: Average crystal grain size of coarse crystal grain part 1 = (1 / t ₂ ) ∫Coarse _{crystal grain part 2} D (z) dz
<D ₁₂ >: Average crystal grain size of coarse crystal grain parts 1 and 2 = (1 / (t ₁ + t ₂ )) ∫ _{Coarse crystal grain part 1 + 2} D (z) dz
<D ₃ >: average crystal grain size of fine crystal grain part 3 = (1 / t ₃ ) ∫fine _{crystal grain part 3} D (z) dz

When defined as described above, the electrical steel sheet according to the present invention has an average of coarse crystal grain portions 1 and 2 existing in both front and back surface layers in order to realize low iron loss in a high frequency range of about 400 Hz to 2 kHz. The crystal grain size <D ₁₂ > and the average crystal grain size <D ₃ > of the fine crystal grain part are represented by the following formula (1):
<D ₁₂ > / <D ₃ > ≧ 2.0 (1)
It is necessary to satisfy.
When there is a portion deviating from the above definition of the coarse crystal grain portion in the vicinity of the steel plate surface (ie, between the position of the line segment L where D = 0.5D _max and the steel plate surface), the thickness (or volume) If the (fraction) is 5% or less of the total thickness, the effect of the present invention is not hindered. Further, as described above, the ratio of the magnetic permeability between the coarse crystal grain portion and the fine crystal grain portion is not necessarily 2.0 or more.

Next, in the electrical steel sheet of the present invention, the total thickness (t ₁ + t ₂ ) of both surface layer portions of the coarse crystal grain portion is 10% or more of the total plate thickness, and the thickness t ₃ of the fine crystal grain portion is the entire plate. It is preferably 10% or more of the thickness. The coarse crystal parts present on both front and back surface portions of the steel plate are portions where the magnetic flux substantially passes mainly in the high frequency range, and the total thickness (t ₁ + t ₂ ) of the front and back surface layers of this portion is the entire plate. If it is less than 10% of the thickness T, the effect of reducing iron loss in the high frequency region cannot be obtained. Further, the fine crystal grain portion at the center of the plate thickness has the effect of reducing the magnetic loss and reducing the iron loss in the high frequency region, and the thickness t _{3 of} this portion is less than 10% of the total plate thickness T. This is because the desired high-frequency iron loss reduction effect cannot be obtained. Here, when the above relationship is formulated into a mathematical formula, the following formula (2) is obtained.
(t ₁ + t ₂ ) /T≧0.1 and t ₃ /T≧0.1 (2)

In the electrical steel sheet of the present invention, the difference in thickness between the coarse crystal grain portions of both surface layer portions is preferably 30% or less of the average thickness of the coarse crystal grain portions of both surface layer portions. The coarse crystal grain portions on the surface of the steel sheet are present in both surface layer portions of the front and back surfaces of the steel sheet in substantially the same thickness, so that an increase in loss due to eddy current can be effectively prevented. The reason is that if the amount of the magnetic flux flowing through the surface layer portion of the steel sheet is different, the eddy current loss is increased due to the non-uniform magnetic flux distribution. Therefore, from the viewpoint of preventing such an increase in iron loss, the difference between the thickness t ₁ and the thickness t ₂ of the coarse crystal grain portions present on both front and back surface portions should be 30% or less of the average value thereof. good. Here, when the above relationship is formulated into a mathematical expression, the following expression (3) is obtained.
| t ₁ −t ₂ | / {(t ₁ + t ₂ ) / 2} ≦ 0.3 (3)

In the electrical steel sheet of the present invention, the difference in average crystal grain size between the coarse crystal grain portions of both surface layer portions is preferably 30% or less of the average crystal grain size of the coarse crystal grain portions in both surface layer portions. For the same reason as described above, the magnetic permeability of the coarse crystal grain portion present in the surface layer portion of the steel sheet is preferably substantially equal on the front and back sides. From such a viewpoint, it is preferable that the difference in the average crystal grain size of the coarse crystal grain portion is 30% or less of the average crystal grain size of the entire coarse crystal grain portion. Here, when the above relationship is formulated into a mathematical expression, the following expression (4) is obtained.
| <D ₁ >-<D ₂ > | / <D ₁₂ > ≦ 0.3 (4)

Next, the manufacturing method of the electrical steel sheet which concerns on this invention is demonstrated.
The electromagnetic steel sheet of the present invention has a coarse crystal grain portion having a high magnetic permeability in the surface layer portion of the steel plate and a fine crystal grain portion having a low permeability inside the steel plate. As a method of manufacturing an electrical steel sheet having a particle size distribution in the plate thickness direction, a single material is used to control precipitates in the plate thickness direction, control of alloy components, surface modification by surface modification such as decarburization, etc. A method such as grain growth control can be used. Alternatively, a method can be used in which a plurality of materials having different initial particle diameters and components are prepared, and the materials are pressure-bonded by rolling a plurality of these materials in hot rolling or cold rolling.

  When the electromagnetic steel sheet of the present invention is rolled and pressure-bonded and manufactured, for example, a material steel strip having a thickness a that finally obtains a coarse crystal structure that satisfies the above-mentioned formula (1) A material steel strip B having A and a thickness b and a material steel strip C having a thickness c capable of obtaining a fine crystal structure are prepared, and these are rolled in three layers like A / C / B. Then, it is preferable to perform pressure bonding. In the case of using hot rolling, these crimp rollings are preferably rolled after heating to 900 ° C. or higher after removing the surface scale. When using cold rolling, it is preferable to roll at a temperature of 150 ° C. or more at a reduction rate of 50% or more after cleaning the surfaces to be joined. The raw steel strips A and B may be the same or different. At this time, in order to satisfy the above-described expression (2), (a + b) may be set to 10% or more of (a + b + c) and the thickness c of the steel strip C may be set to 10% or more of (a + b + c). Further, in order to satisfy the above-described expression (3), the absolute value | ab− of the difference between the thicknesses of the steel strips A and B sandwiching the steel strip B may be set within 30% of (a + b) / 2. . Furthermore, in order to satisfy the above-mentioned equation (4), the material steel strips A and B and the material steel strip C are subjected to finish annealing under the same conditions as the manufacturing conditions, and the component composition of the material in advance to satisfy the equation (4). Etc. are preferably adjusted in advance.

  In the above description, the electromagnetic steel sheet having a three-layer structure has been described as an example. However, the present invention is not limited to the three-layer structure, and for example, between A and C and / or between B and C. In addition, a material steel strip from which an intermediate structure of coarse crystal grains and fine crystal grains is obtained may be interposed to form a structure of four or more layers.

(Reference example)
C: 0.07% by mass, Si: 3.0% by mass, Mn: 0.5% by mass, Al: 0.5% by mass, the balance is made of steel composed of Fe and inevitable impurities, and a steel slab is obtained by continuous casting. This steel slab was hot-rolled and cold-rolled to form a cold-rolled steel strip having a sheet thickness of 0.35 mm. The cold-rolled steel strip was recrystallized at a temperature of 700 ° C., and then subjected to continuous annealing in which a surface layer portion was decarburized in a 900 ° C. decarburizing atmosphere, thereby generating coarse crystal grains on the surface layer. At this time, the thickness and the grain size of the coarse crystal grain portion generated on the steel sheet surface layer were changed by variously changing the annealing temperature. Thereafter, an insulating coating was applied to the surface of the steel sheet to obtain a product, and about 500 g of an Epstein test piece was cut out in half from the rolling direction and the direction perpendicular to the rolling direction, and magnetic measurement was performed according to JIS C2550.

The results of the measurement are shown in Table 1. FIG. 2 shows the ratio of the average crystal grain size of the coarse crystal portion to the fine crystal portion when the thickness of the coarse crystal grain portion is 60% of the total plate thickness and the thickness of the fine crystal grain portion is 30% of the total plate thickness. _{<D 12> / <D 3} > and showing the relationship between iron loss _{W 10 / 1k.} From Table 1 and FIG. 2, the electromagnetic steel sheets of Example, iron loss _{W 10 / 1k} has reduced, satisfy (1) above and (2) the relationship especially, No. Particularly low iron loss values have been obtained for samples 5-8, 10 and 12.

  After melting steels having three kinds of component compositions A to C shown in Table 2 and making them steel slabs by continuous casting, these steel slabs were hot-rolled and cold-rolled to obtain various cold sheet thicknesses. A steel strip was produced. As shown in FIG. 3, these cold-rolled steel strips are stacked to form a three-layer structure in which the steel strip A or B is the outer layer 1 or 2 and the steel strip C is the inner layer 3, and then heated to 200 ° C. However, it was cold-rolled and pressure-bonded to obtain a steel sheet having a thickness of 0.50 mm, and then annealed and coated with an insulating film to obtain a magnetic steel sheet. About 500 g of Epstein test pieces were cut out from these steel sheets in half from the rolling direction and the direction perpendicular to the rolling direction, and magnetic measurements were performed according to JIS C 2550. Further, the cross section of the product plate was examined, and the average crystal grain size and thickness of the coarse crystal grain part (outer layers 1 and 2) and the fine crystal grain part (inner layer 3) were measured.

  Table 3 shows the combinations of the steel strips and the measurement results of the magnetic characteristics, average crystal grain size, and thickness. From Table 3, the iron loss decreased in Nos. 14 to 19 satisfying the formula (1) of the present invention, and in particular, No. 14 satisfying all the above-described formulas (1) to (4) of the present invention. It can be seen that at ˜16, the iron loss value is greatly reduced.

The electromagnetic steel sheet according to the present invention is used as an iron core material for motors and generators, and particularly reduces iron loss in a high frequency range of 400 to 2 kHz and contributes to high efficiency.

It is a schematic diagram explaining the crystal grain size distribution of the electromagnetic steel plate cross section of this invention. It is a graph which shows the influence which the ratio of the average crystal grain size of a coarse crystal grain part and a fine crystal grain part has on iron loss. It is a schematic diagram which shows the cross-section of the steel plate rolled and crimped | bonded in Example 2. FIG.

Claims (2)

An electrical steel sheet containing 0.010 mass% or less of C and 4 mass% or less of Si, wherein both surface layer portions of the steel sheet have coarse crystal grain portions defined as follows, and a central portion in the thickness direction Has a fine crystal grain portion defined as follows, and the ratio of the average crystal grain size between the coarse crystal grain portion and the fine crystal grain portion is 2.0 or more, and the coarse crystal grain The total thickness of both surface layer portions of the portion is 10% or more of the total plate thickness, and the thickness of the fine crystal grain portion is 10% or more of the total plate thickness (however, the plate thickness is 0.08 to 0.22 mm) Electrical steel sheet characterized by the above.
When the distribution in the thickness direction of the average grain size D in a plane parallel to the surface of the steel sheet is measured, the maximum value is D _max and the minimum value is D _min .
Coarse crystal grain part: part satisfying D ≧ 0.5D _max Fine crystal grain part: part satisfying D ≦ 2.0 D _min In the coarse crystal grain portion, the difference in thickness between both surface layer portions is 30% or less of the average thickness of both surface layer portions, and the difference in average crystal grain size between both surface layer portions is 30% of the average crystal grain size of both surface layer portions. The electrical steel sheet according to claim 1, wherein:

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